A A330-300, instead of a Airbus A340-600, the same plane the airline typically uses during the winter. The move was widely expected, as Lufthansa is now competing against US Airways instead of working with it.
Note that “smaller” here is a relative term. Lufthansa doesn’t really do small on its transatlantic flights. The smallest aircraft it uses in that role is the Airbus A340-300 and A330-300 — both have the same length fuselage, the difference is the number of engines and range. (The A340-600 is a stretched A340-300.) The largest aircraft US Airways has is the Airbus A330-300.
Lufthansa also has a new denser product out called Jump. It isn’t planning to fly aircraft in the Jump configuration to Charlotte at this time.